The present invention relates to film laminates which are particularly impermeable for gas, and to the use of these gas impermeable film laminates as wrapping material of vacuum insulation panels.
In some special technical products, such as e.g. in the production of vacuum insulation panels (VIPs), films are needed which possess extremely low gas permeability values to guarantee that the vacuum, once applied, and thus the serviceability of the VIPs, is maintained over a very long period (10-15 years).
Conventional barrier films made of plastics, as described e.g. in EP-A 0 517 026, do not achieve the gas barrier effect needed. Composites containing an aluminium foil, while they do possess a total gas barrier, are undesirable in many applications because of the thermal conductivity of aluminium.
In addition, metallised films or films vapour-coated with SiOx are known which avoid the disadvantages relating to the thermal conductivity of the pure metal foils (as described e.g. in EP-A 0 878 298), and achieve higher barrier effects than pure plastic films, but their values are also a long way from the gas barrier values required.
Vacuum insulation panels (VIPs) here mean sheet-like objects which consist of an insulating material and/or filler and are wrapped in a high-barrier film by vacuum packing. The type, and particularly the level, of the vacuum here are dependent on the insulating material or filler used and on the insulating action required of the VIP. Over the service life of the VIP, the wrapping with a high barrier film prevents the diffusion of gases, which impair the vacuum and thus the insulating properties of the VIP. Metal foils are undesirable as the high-barrier films, since these conduct heat over the edges of the sheet-like VIP and thus reduce the insulation performance.
The object of the present invention was therefore to provide film laminates which achieve a particularly high gas barrier effect without using thermally conductive metal foils as components. At the same time, mechanical and thermal properties of the film laminate should be improved. In particular, film laminates suitable for the production of vacuum insulation panels (VIPs) should be provided.
According to the invention, this is achieved by providing of a multi-layer film laminate comprising at least 4 layers (I) to (IV), arranged directly or indirectly in the following sequence:
layer (I) as one surface layer of the film laminate comprising at least one layer vapour-coated with aluminum or SiOx or a metal oxide from the main groups 2 or 3, whereby the vapour-coated surface is adjacent to the following layer,
layer (II) as a gas barrier layer of resin,
layer (III) comprising at least one further layer vapour-coated with aluminum or SiOx or a metal oxide from the main group 2 or 3 and
layer (IV) as a heat-sealable layer, which is the other surface layer of the film laminate.
It would be expected for the gas barrier effect of the film laminate according to the invention to be provided by the gas barrier effect of the individual film with the lowest permeability, or to be calculated from the sum of the barrier effects of the individual films, but surprisingly, gas barrier effects are achieved which are not only distinctly higher than those of the individual films but are even higher than those of the sum of the individual films.
In order to obtain even further increased gas permeability values the film laminates according to the invention can contain the layer (I) and/or the layer (III) preferably more than one time, and this layer or these layers can be vapour-coated or not vapour-coated with aluminium or SiOx, with x for 1-2, preferable 1.5-1.8, or a metal oxide from main groups 2 or 3 and the vapour-coated surfaces of the layers (I) and/or (III) are preferable adjacent to each other.
The layers vapour-coated with aluminium or SiOx or a metal oxide from main groups 2 or 3 can consist of any conventional thermoplastic resins, particularly of resins of at least one polyester, polyamide, polyolefin or a copolymer thereof. These layers (I) and/or (III) can also consist of a coextrudate of different polymers, which consists of at least one layer, particularly two layers of one of the above mentioned thermoplastic resins, and a gas barrier layer of resin, particularly of a hydrolysed ethylene vinyl acetate (EVOH) with 25-45 Mol-% vinyl acetate and is sandwiched particularly between two layers of the mentioned thermoplastic resins. The thickness of the individual layers (I) and/or (III) and the each entire thickness is not essential, but can influence the gas barrier effect to a small degree and will help to determine the mechanical and thermal properties of the film laminate.
With the film laminates according to the invention oxygen permeability values of less than 0.1 cm3/m2 d bar (23xc2x0 C., 75% r.h.), in particularly of less than 0.05 and in particularly of xe2x89xa60.01 and water vapour permeability values of xe2x89xa60.1 g/m2 d (38xc2x0 C., 90% r.h.) can be achieved. The oxygen permeability is determined according to DIN 53380-3 and the water vapour permeability according to DIN 53122. Through the combination of different layers, not only can the gas permeability values be adjusted to the values required by the application, but it is also possible, by modifying the material of the layer vapour-coated with aluminium or SiOx or a metal oxide from main groups 2 or 3, to vary the mechanical and/or thermal reference values of the resulting film laminate according to the invention.
If a polyamide vapour-coated with aluminium or SiOx or a metal oxide from main groups 2 or 3 is arranged as the surface layer (I), the resulting film laminate is also distinguished, in addition to the low gas permeability values, by high mechanical stability, particularly by high puncture resistance which offers advantages in the handling of the film laminates according to the invention and thus prevents damages of the laminate during wrapping. The VIPs must, in some cases, withstand large mechanical loads, both during manufacture and during installation in the final application, which can lead to damage to the wrapping and thus to the gas barrier properties.
A layer based on polypropylene vapour-coated with aluminium or SiOx or a metal oxide from main groups 2 or 3 which is distinguished by a particularly good water vapour barrier is preferably selected as the outer layer (I). If this outer layer is combined with a layer (III) consisting of a polypropylene layer vapour-coated with aluminium or SiOx or a metal oxide from main groups 2 or 3, which is also distinguished by a particularly good water vapour barrier, the film laminate according to the invention formed therefrom will be distinguished both by a better water vapour barrier compared with the individual polypropylene layers and by an extremely improved oxygen barrier, since the inner gas barrier layer (II) of polyvinyl alcohol is protected from being damaged by water vapour.
One or more of the layers (I) and/or (III) vapour-coated with aluminium or SiOx or a metal oxide from main groups 2 or 3 is also preferably a coextrudate, which consists of at least one layer (a) of polyamide and at least one gas barrier layer (b) of resin. A 3-layer coextrudate as layer (I) and/or layer (III) of polyamide as the outer layers and hydrolysed ethylene vinyl acetate copolymer (EVOH) as oxygen barrier layer inbetween is particularly suitable. The gas barrier layer ensures extremely improved gas barrier values in the resulting film laminate according to the invention, and particularly when EVOH is used as the gas barrier layer the oxygen barrier values are improved.
In a particularly preferred combination, one or more of the layers (I) and/or (III) are vapour-coated with aluminium, preferably in a thickness of 30 to 80 nm.
Homo- or copolyolefins can be used as material for the heat-sealable layer (IV). Linear low density polyethylene (LLDPE), low density polyethylene (LDPE), metallocenic polyethylene, polypropylene (PP), polybutylene (PB), ethylene vinyl acetate copolymers (EVA), high density polyethylene (HDPE), ionomers (IO) and mixtures of these substances, and also amorphous polyester and amorphous polyethylene terephthalate (aPET), are preferred. A multi-layer coextrudate of the heat-sealable layer (IV) of the above materials is also possible according to the invention. The thickness of the heat-sealable layer (IV) is preferably 20 to 200 xcexcm, particularly 50 to 100 xcexcm.
The film laminate according to the invention used for the production of VIPs comprises preferably a heat-sealable layer (IV) of a free-flowing material, particularly an ionomer, that guarantees particularly gas-tight sealed seams under the dusty production conditions typical of VIP manufacture.
For the bond between the individual layers of the laminate according to the invention, commercial reactive adhesives, such as in particular 2-pack polyurethane adhesives, are preferably used. However, polyolefinic adhesion promoters, preferably polyethylene, ethylene ethyl acrylate (EEA) or ethylene methyl methacrylate (EMMA), can also be used. The gas barrier effect of the film laminate according to the invention is not substantially dependent on the type of bond between the individual layers, however.
In the case of the use of the two-pack polyurethane adhesives in particular, it should be ensured that the component composition is selected such that the lowest possible generation of gas takes place.
A further object of the invention is the use of the inventive film laminates as high barrier films, in other words almost gas impermeable barrier films, as wrapping of vacuum insulation panels.
A further object of the invention are vacuum insulation panels with an inventive film laminate as gas tight wrapping of an insulating material or filler. Any type of insulating materials or fillers, as conventionally used in vacuum insulation panels, is possible, particularly an insulating material of polyurethane foam or polystyrene foam each with open cells and/or a filler material of silicium oxide.
Examples of film laminates which describe the film laminates according to the invention in more detail, but which do not limit the scope of the invention, are reproduced below.